1. Field of the Invention
The invention relates generally to coated articles having useful optical properties and particularly to reflective coated articles suitable for the manufacture of optically reflective components of lighting fixtures including parabolic louvers and the like.
2. Description of the Prior Art
The reflective surfaces of lighting fixture components have long been the subject of intense study especially for light control in continuing efforts to maximize the efficiency of lighting fixtures, improve the appearance of such fixtures and to reduce costs. Whether the lighting fixture component under consideration is taken to be a downlighting reflector or a reflective louver, a primary factor involved in the performance of the reflective fixture component is the material from which the component is manufactured. A primary example is the family of parabolic luminaires manufactured and marketed by Lithonia Lighting, Inc. of Conyers, Ga. under the registered trademark PARAMAX among other trademarks registered by National Service Industries, Inc. of Atlanta, Ga., of which Lithonia Lighting is a division. Particular lighting fixtures manufactured and marketed by Lithonia Lighting, Inc., include fluorescent parabolic troffers including both recessed and surface-mounted fixtures. The performance of such parabolic lumenaires is owed in large measure to the precise parabolic shape of a louver component typically constructed of reflector-quality aluminum such as anodized aluminum . A louver constructed for use with a parabolic lumenaire is provided with carefully contoured cells in order to achieve uniform light distribution, minimum high-angle brightness, reduced glare and optimum efficiency. Such louvers are shaped in the manner of tangential parabolas for superior light control, available light being concentrated to a greater degree in those photometric zones most crucial to comfort and efficiency especially in a task lighting situation. Contoured portions of the lumenaire housing continue the paraboloid shapes of the louver to envelope a fluorescent light source or other suitable light source in a fully reflective cavity.
Louver structures are disclosed in a large number of previously issued United States patents. As an example, U.S. Pat. No. 4,780,800, to Mullins, discloses reflective louvers used in lighting fixtures, the louvers of Mullins having reflective parabolic or other curved surfaces. The structure disclosed by Mullins is essentially exemplary of parabolic louvers and similar reflective lighting fixture components which are very well known in the art. Additionally, Wall, Jr. in U.S. Pat. No. 4,839,778, discloses a louver system which is also exemplary of prior art parabolic lumenaires. Still further disclosure is provided by Caferro, in U.S. Pat. No. 5,008,791, wherein parabolic louvers are disclosed as components of parabolic lumenaires and the like. The principles of parabolic louvers and resulting light distribution effects are detailed in U.S. Pat. No. 2,971,083 to Phillips et al. In this patent, the function of parabolic louvers is set forth in addition to the disclosure of other reflective components of lighting fixtures generally and parabolic lumenaires or parabolic troffers in particular. Lasker, in U.S. Pat. No. 4,907,143, describes a fluoescent troffer having a reflector system, the reflectivity of which is of substantial import in the performance of the troffer described in the patent.
Common practice in the lighting industry has been to form reflective lighting fixture components from materials such as anodized aluminum, it especially being the prior practice to form reflectors per se and louvers among other components from anodized aluminum which is an extremely costly material. In spite of material costs, anodized aluminum has proven to be an effective material for manufacture of reflective lighting components due not only to the optical qualities of the material but also due to the ability to readily form anodized aluminum into those shapes necessary for use as reflective lighting fixture components. The specular nature of anodized aluminum can also result in fixture characteristics which are less desirable than would be optimum. For example, witness marks as well as fingerprints and the like inherent in the manufacture of lighting fixtures using anodized aluminum can cause deficiencies in appearance. Further, anodized aluminum is subject to cracking and crazing at elevated temperatures such as are encountered in automated washing apparatus currently available for the cleaning of louvers after manufacture on an assembly line. Due to the expense of anodized aluminum, a material capable of substituting for anozided aluminum in the manufacture of reflective lighting fixture components would be welcomed in the art even if the only advantage of such a substitute material would be lower cost. However, in order to realistically substitute for anodized aluminum, a substitute material would necessarily exhibit desirable optical properties as well as be capable of forming with currently available punching and forming tools used in the manufacture of reflected components previously formed of anodized aluminum and the like. In other words, a material capable of substitution for anodized aluminum in the manufacture of reflective lighting fixture components would require properties essential for ease of manufacture, assembly, installation and even long term maintenance and would be especially welcomed in the industry by improvement in these necessary characteristics when compared to anodized aluminum which is presently the material of choice. The industry would further enthusiastically receive a material having the appearance of an anodized aluminum, low irridescent semi-specular finish. The present invention provides a material particularly useful for the fabrication of reflective lighting fixture components and which enjoys the advantages so enumerated as well as a number of other substantial advantages as will be described in greater detail hereinafter.
The materials referred to herein for manufacture of reflective lighting fixture components generally comprise coated articles having optically useful reflective properties and which are essentially formed from highly polished substrates which reflect light in a specular manner and which are coated such as with a polymeric "clearcoat" coating which acts to combine with the specular surface of the substrate to create a compound reflector which exhibits all three reflective components, i.e., specular, spread and diffuse, to obtain the appearance and optical distribution associated with low irridescent, semi-specular anodized aluminum and wherein the specular reflective component dominates but which has a sufficient diffuse component to provide brighter surface appearance, minimized glare, etc. in the finished lighting fixture having at least certain reflective portions formed of the coated substrates of the invention. It is to be stressed that polymeric "clearcoat" coating materials exist in the art as do coated reflective substrates. An example of a polymeric clearcoat is provided in U.S. Pat. No. 5,262,494, to Smith et al and assigned to Morton Coatings, Inc. of Chicago, Ill., the disclosure of this patent being incorporated hereinto by reference. Morton Coatings, Inc, and parent company Morton International, Inc. provide an extensive line of coating materials including clearcoat materials under the trademarks MOR-BRITE and other trade designations. Such coatings have particular utility in the manufacture of coated articles formed according to the invention and used for the manufacture of reflective lighting fixture components. The prior art is also replete with coated reflective materials. As an example, U.S. Pat. No. 3,499,780 to Etherington et al discloses the coating of an aluminum reflector having a specular reflecting surface having a silicate solution applied thereto followed by heating to produce a silicate coating on the specular reflecting aluminum surface. However, the material described by Etherington et al has not proven useful in the manner of the present materials as a substitute for anodized aluminum in the manufacture of reflective lighting fixture components. Coated aluminum reflective articles are also disclosed by Mason in U.S. Pat. No. 2,108,604, this patent providing a durable surface on reflective aluminum by particular cleaning processes followed by anodic oxidation. Cohn, in U.S. Pat. No. 2,729,551, treats an aluminum surface to produce a macroscopically uniform smooth finish in an effort to provide optically useful reflective materials. Ricchezza, in U.S. Pat. No. 3,625,737, provides a protective coating on a reflective aluminum substrate while Korver, in U.S. Pat. No. 3,372,008 also provides a reflector formed of aluminum and having a protective layer formed thereon. These prior art reflective materials do not provide acceptable substitutes for the anodized aluminum currently employed in the manufacture of reflective lighting fixture components such as downlighting reflectors, parabolic louvers, etc.
The coated articles of the present invention find particular utility in the formation of components of lighting fixtures which are intended to have optically useful reflective properties and which can be readily manufactured using available forming tools. The materials comprising the coated articles of the invention provide a number of advantages in finished lighting fixtures including fluorescent troffers and the like due not only to the lower cost of the material relative to presently used anodized aluminum but also due to improvements in appearance and other optical characteristics. Accordingly, the invention provides solution to long-felt needs in the art as will be more fully described hereinafter.